feat: Sprint 2 - 概率语义 + 轻量快照 + 数据库约束

P0-05: confidence → subjective_confidence 改名(15 文件)
       LLM 主观置信度与概率分离
P0-02: predictions 增加 cutoff_at + input_hash(轻量快照)
       MatchContext 暴露 match_dt
       单/多 Agent 路径均记录快照元数据
P2-05: 数据库 CHECK 约束
       - pred_home_goals >= 0
       - pred_away_goals >= 0
       - subjective_confidence 0~1
       - pred_1x2 IN (1,X,2)
       - mode IN (single,multi)
P2-06: limit 分页约束(ge=1, le=200)
P2-01: 新增 /health/ready 就绪检查

src/llm/eval.py

@@ -61,8 +61,8 @@ async def get_eval_summary() -> dict:
                 err = ((p.pred_home_goals - p.actual_home_goals) ** 2 +
                        (p.pred_away_goals - p.actual_away_goals) ** 2) ** 0.5
                 b["score_errors"].append(err)
-            if p.confidence is not None:
-                b["conf_sum"] += p.confidence
+            if p.subjective_confidence is not None:
+                b["conf_sum"] += p.subjective_confidence
                 b["conf_count"] += 1
 
         summary = []